1. Field of the Invention
The present invention relates generally to a semiconductor devices and, more specifically, to methods for fabricating semiconductor devices.
2. Description of Related Art
Generally, semiconductor devices are fabricated by forming a plurality of material layers on a semiconductor substrate and subsequently patterning the material layers. As used herein, the “front side” of the semiconductor substrate refers to the side of the semiconductor substrate on which semiconductor devices are formed and the “back side” refers to the opposite side of the substrate. As layers are being formed on the front side of the substrate, material layers similar to the front side material layers may be formed on the back side of the semiconductor substrate. The material layers can apply tensile stresses or compressive stresses to the semiconductor substrate. If material layers having the same components and thicknesses were formed on the front and back sides of the semiconductor substrate, then the semiconductor substrate may maintain its original shape because stresses on the front and back sides of the substrate are balanced. However, warpage of the semiconductor substrate may occur when the forces on the front and the back sides of the semiconductor substrate are not balanced.
FIG. 1 and FIG. 2 are fabrication processes for illustrating a method for fabricating semiconductor devices according to the prior art.
Referring to FIG. 1, a semiconductor substrate 10 having a front side 10a and a back side 10b is prepared. Semiconductor devices are formed on the front side 10a of the semiconductor substrate 10. The semiconductor devices may be formed on a silicon substrate, a silicon germanium substrate, a SOI substrate, etc.
Referring to FIG. 2, at least one material layer is formed on the semiconductor substrate. A predetermined structure 14 can be formed by selectively patterning the material layers on the front side 10a of the substrate to. The material layers may include various types of materials, such as oxide, nitride and the like. The materials layers can be formed through various deposition processes. For example, the oxide layer may be formed by a thermal oxidation process. As the material layers are formed on the front side of the semiconductor substrate 10, similar material layers 12 can be formed on the back side of the semiconductor substrate. Accordingly, the stresses applied to the front and back sides may not be balanced if the predetermined structure 14 is formed by pattering material layers on the front side of the semiconductor substrate 10 without patterning the corresponding layers 12 on the back side of the semiconductor substrate 10. As a result and as shown in FIG. 2, warpage of the semiconductor substrate 10 may occur.
Increased warpage of the semiconductor substrate may reduce pattern uniformity of the semiconductor substrate. Yield may be decreased, and furthermore, the semiconductor substrate may be broken down.
These problems may be more prevalent in large diameter wafers, such as wafers having a 300 mm diameter or more. Such large diameter wafers may have increased warpage depending on tensile stress or compressive stress.